IP V6 video broadcast / on-demand system Tsinghua University Yuan Chao Wang Zhiguhua Dai Qionghai 01-5-30 11:31:03
VOD system exists
With the development and popularity of the Internet, Internet access has become part of people's daily lives. However, the services provided by the current network are much larger than the previous year, but basically stayed on email and home browsing and text conversation. The main reason for this happens is that the current Internet is also based on narrowband networks, and cannot achieve large data transmission.
It can be seen that there are two trends in the current network development: the rapid growth of the number of users and the multimedia of network services. People will pay more attention to interactive multimedia information services. To achieve this, you must have two conditions: high network bandwidth and protocols suitable for multimedia information transmission.
Under current network conditions, there are two channels for multimedia video / audio broadcasts: Internet and cable TV. But they all have a weakness of overcoming, because many of these two networks are not expected to be in early design, so it is also the weakness of the network, which is difficult to overcome other than complete transformation.
1. INTERNET exists
The Internet is developed in the early 1990s and based on IP V4. Since the early Internet is mainly used for research, the transferred data is primarily based on text, and the designers have not taken into account the company's joining and today's scale. Today, in today's demand, existing internets have multiple transformations and bandwidth expansion, but still unable to meet the current and future needs.
Relatively, the impact of bandwidth seems to be less obvious, because my country's national conditions are in terms of internets, most of the network trunk lines are used in fibers, and some newly built cells also use fiber optic home programs. Plus the continuous expansion, so we have reason to believe that the bandwidth of at least a range will not become an obstacle to development. Its fundamental defect is concentrated in the following aspects:
(1) The address space is serious, and the multicast function is limited. With the explosive growth of users on the Internet, the limitations of address space are growing. Future three-grid one is an inevitable trend. Users who participate in video broadcasting and on-demand will be the current number of cable TV users, and now the address space is obviously not enough. IP V4 uses a 32-bit address that cannot overcome this issue. In addition, the techniques of video broadcasting and on-demand on the Internet are mainly multicast, but IP V4 protocols are rarely supported by multicast, and there is still a specific implementation in practical applications. A obvious place is based on IP V4 routers. There is support for multicast function.
(2) Data transmission lacks service quality (QoS) guarantee. Many people think that the bottleneck of the network is bandwidth, as long as the bandwidth problem is solved, then everything is solved. Actually this kind of view is wrong. First, the network bandwidth is unable to fully meet the needs of each person for a long time. Even if the fiber is arriving, the backbone is also unbearable. In fact, future network multimedia information services need to be implemented for each user's request, so different service types can be used for different data types, which may be well used in current limited network bandwidths. Implement multimedia data communication services. The above-mentioned demand is attributed to a point is the requirements of multimedia communication on service quality.
Service quality is usually concentrated in the following four aspects:
● A certain bandwidth requirement. For example, a program of MPEG-2 is transmitted, and the bandwidth of each program is about 6 Mbps.
● Lower end-to-end delay. For video programs, if the delay is too large, it will cause the program to be intermittent, which is unacceptable.
● Delay variations are within a certain range. If it is too large, the receiving end will generate the overflow or fall overflow of the data, which affects the quality of the viewing.
● Broken rate and acceptable error can be accepted (no retransmission). For multimedia data communications, re-transfer is impossible, which will cause unacceptable delays in data transmission. Therefore, there is only a data error to be discarded, but it can be controlled within a certain range, allowing the user to be accepted. (3) Data security is difficult to guarantee. The security of the network is also the need to consider. For video point broadcast, generally use the user's point to broadcast the payment, so the played program should be encrypted, otherwise it will be seen free of charge by other users; if the online payment fee is used, the encryption of user data will be very important. At present, the encryption method used by the network is mostly in the application layer, which is relatively low in the safety factor of the encryption method. This is because IP V4 does not consider data security factors when designing.
2. Cable TV network VOD system exists
For the main problem with the current telecommunications network - with a narrow bandwidth, some people have proposed a program for multimedia data communications with cable television networks. Its advantage is that the network band is large, and each family has been completed, so it is still relatively fast on it. But there is a lot of difficulties to achieve point broadcast because it requires uplink channels to implement feedback from user on-demand information. To achieve this, you need to modify the current cable TV network. The price of this transformation is high, and there is currently only some of the communities that have more economic developed cities to achieve this transformation. Especially for interactive video conferences such as bidirectional transmission requirements, it is difficult to achieve with the current cable TV network.
In addition, cable TV is due to lack of flexible software (because most components are implemented by hardware), the adopted encryption algorithm must lack flexibility and diversity, and the possible possibility is more likely.
Advantages of IP V6
IP V6 is a new protocol that the next-generation Internet will adopt, which is formed by modifying and expanding on the IP V4, and is currently being promoted. It can effectively solve problems existing on the Internet to implement multimedia services. At present, there are several world-wide experimental networks, such as NGI, VBNS, Internet2, 6bone and other backbone. The new generation of routers have also begun to support IP V6.
(1) Upgrade from IP V4 to IP V6, address space has a major improvement in capacity or type. IP V6 uses a 128-bit Internet address, which means that the address space will be 3.4 × 1038, which is enough to configure an IP address for each mobile device, and no longer addresses the intersection. The address change of IP V6 is not a simple significance, but a modification of the original address structure. The address structure of IP V6 can improve the circuit efficiency, thereby reducing the burden of the router, increasing data throughput, which is required for the transmission of large data.
(2) IP V6 enhances multicast function. The meaning of multicast is that only the user will join the corresponding multicast group to receive information sent to the group, which is especially significant for the transmission of video programs. The channel concepts in the analog TV can be replaced by the concept of the multicast group, and the range of multicast groups can include nodes in any location in the same local network, the same mechanism, and even anywhere in the IP V6 global address space. This provides greater flexibility for network multimedia information services.
(3) IP V6 considers QoS. The IP V6's cladding structure has changed, which uses business flow fields and stream signature segments. The business stream is expanded to 1 byte so that 256 levels of priority can be defined, and various multimedia information determine the priority of the packet according to the emergency situation, thereby ensuring that each service can meet the quality of users. IP V4 is described as an unconnected protocol. Since IP V4 has no correlation between the same data stream package and the package of the same data stream in order to let each package find their own path to reach the destination address, the intermediate router has been handled separately for each package, the result is the same Two packets before and after business flow may be through different paths to reach the destination address. For each package, it will increase the processing time of each package, and for file transmission, the application may not affect, but for video broadcasting, the delay increase and uncertainty will result in a serious decline in quality. In IP V6, all packets of the same business stream use the same stream tag so that when the router detects the same stream tag, the same path is transmitted, without having to re-select the route for each packet, thereby greatly Improve the efficiency of packet forwarding and reduces the delay of end-to-end. (4) IP V6 improves the error rate and encryption. In the case where the hardware structure and the agreement, the decrease in the error rate is a great relationship with the encoding method. It is currently used by MPEG-2 encoding.
Since the encryption method adopted by IP V6 is to put the encrypted information in the IP layer, this is a relatively low data transfer, so there is a better effect for the current application layer encryption method.
One advantage of using Internet Multimedia Data Services is that it provides more complete additional information. Although the DVB standard specifies Si information, due to limited interaction of cable TV, it is impossible to provide colorful content as an Internet, and a lot of information about the program, and because of the difficulty of implementation (including the organization of program information, The user's top box contains information retrieval of the downlink data stream), so there is currently very small features of the DVB VOD system. However, it is different from the Internet. Due to the huge flexibility of the software, the multimedia information contains complex additional information, especially the appearance of MPEG-2, MPEG-4, MPEG-7, enables efficient organization and retrieval of multimedia information. Utilization is possible, using the Internet to implement the current cable TV online DVB Electronic Program Guide (EPG) feature will be more simple and valid, and you can provide users with more content and options.
IP VOD implementation
1. Traditional implementation
In the current situation, there are two ways to achieve digital cable TV:
The first is that all program channels are transmitted to the user's set top box, and the user selects the program channel you want to watch on the set top box. This method is relatively simple, and the demultiplexing of the program stream is done in the set top box. At present, most digital cable television systems use this method, and the client is an HFC access method. However, the current HFC is not suitable for interactive two-way data transmission services, and the cost of two-way transformation is too high.
The second is to adopt SDV (Switch Digital Video), and its main application occasion is "Fiber to the Roadside (FTTC) and Coaxial Cables." The bandwidth is subject to the bandwidth of the coaxial cable, only one way to reach the user's set top box. This structure is simple for set top boxes, but greatly increases the complexity of the main digital terminal (optical fiber and equipment between the cables of each home user).
2. Implementation of IP VOD
(1) Basic requirements are similar to the INTERNET-based video data transmission system and the second way, and the end user receiver is also all the way, rather than sending all the programs to the user. But there is the following differences:
● Transfer MPEG-2 stream data is an IP package;
● The transmission of program data is multicast mode; ● The channel selection is to leave a multicast group to add another multicast group.
The way to control the user selection group is to send a set-top box to the multicast router or multicast access server, which is responsible for the user to join or leave a multicast group. In fact, there is a router acting as a querier in each multicast group, and you can determine the multicast group where the user is located according to the user's choice by sending group member packets, and updating the multicast group member. Program channel).
From the backbone network, the current Gigabit network can accommodate 150 digital program channels at the same time, with a bandwidth of each channel to 4m to 6MHz. From the user's access, because only single program enters the user home, it does not need to fiber to the household, but at least 25Mb / s VDSL access is necessary, because the user's home may have multiple television and PCs Internet. In addition, this access speed is also required for high-definition TVs that will be opened.
(2) QoS guarantee that providing multimedia digital services is a very important point to service, specifically, pay attention to the following aspects:
● Advanced images and sound programs are not at least poor than satellite TV.
● The channel selection is small, the expected value is within 1 second;
● Support the content content that is not available in general cable TV, such as video on demand;
● Friendly user uses the interface.
A good video program service is inseparable from a perfect Electronic Program Guide (EPG), which is an interface that users use multimedia digital services. A perfect EPG allows users to easily enjoy the comfort and convenience brought by multimedia digital services; but a bad EPG will make users lose patient, thus abandon service providers.
MPEG-2 defines the PSI table for program and service information, but there is no specific implementation of its specific implementation. This aspect is to increase flexibility and give various manufacturers a certain development space, which is good in competition. Solution; on the other hand, it is also a description method that has not been better for multimedia information. I believe that with the formulation of MPEG-7 standards, the description of multimedia information will be more accurate and convenient.
In addition, the DVB standard specifies the service information table (SI) of Digital TV Programs, including the Network Information Table (NIT), Climbing Table (BAT), Service Description Table (SDT), and Event Information Table (EIT), etc. They can better describe each program and related programs. At the current phase, since most of the information about the program is still based on text rather than multimedia objects, we can refer to the SI table structure of the DVB to form a program describing the data structure in accordance with the MPEG-2 standard, thereby forming an EPG on the IP online. It can include the following aspects:
● List of programs within a certain time;
● Program query function;
● Simple channel switch interface;
● Video on-demand interface;
● Payment mode selection interface.
(3) A main problem with real-time measures to use IP network for video data transmission is real-time. Since the network based on the server and router is "soft", it is not "hard time" like hardware-implemented cable TV, so the amount of data transmission may change significantly at different times, if the received The data is directly played, and the playback quality will be poor. The method of solving this problem is to implement data buffer at the router or user receiver, and of course the network quality needs to ensure that the buffer does not overflow and overflow, which is not a difficult thing in IP V6 network.
There are three ways to achieve a soft time:
● Hard guarantee: The quality of service specified by the user must obtain 100% guarantee. It generally requires network bandwidth to meet the maximum demand value, and do this cost is very high, and it is not very real.
● Based on statistical law: user-designated service quality can be guaranteed within a certain range, especially for video program services, often does not require 100% accurate data. A certain range of bit error rates and packet loss rates are acceptable. ● Try to guarantee: This is a guarantee that is guaranteed unless the bandwidth is large enough, otherwise it is impossible to perform quality assurance video programs in this case. However, the accuracy is the most important for transactions that are not high in real-time requirements, and this transmission method is also correct. Since IP V6 has added a regulation of service quality, it is entirely possible to implement a soft realistic time using the second method. The router can be used to ensure different processing methods for different business stream categories (data streams can be specified by the user) to ensure user viewing quality.
IP V6 implementation QoS protocol is the IETF resource retention protocol (RSVP). It allows a host to request data streams or processes from specific application (refer to streams that can be identified by routers or data forwarding hosts, in the IP V6 protocol, is a network specified service quality of the same stream label). As the maximum bandwidth based on the average, the host can specify a specific network service level, which is similar to the concept of the network information table in DVB.
It can be seen that in the case where the network bandwidth, the program's EPG, the data transmission QoS, and the corresponding transmission, the receiving software is guaranteed, and a complete IP V6-based video program broadcast / on-demand is now established under certain user scale. The system is completely realistic.
